Stabilized halogen-containing olefin polymer compositions and melamine pyrophosphate stabilizers therefor



United States Patent ()fiiice 333mg Patented July 18, 1967 3,331,808 STABILIZED HALOGEN-CONTAINING OLEFIN POLYMER COMPOSITIONS AND MELAMINE PYROPHOSPHATE STABILIZERS THEREFOR Hendn'kus J. Oswald, Morristown, and Edith Tun, Livingston, N.J., assignors to Allied Chemical Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Mar. 2, 1964, Ser. No. 348,782 4 Claims. (Cl. 260-453) This invention relates to the stabilization of halogencontaining polyolefins against the harmful efiects of high temperatures. More particularly it relates to new chlorinated polyethylene compositions having good thermal stability.

It is known that halogen-containing polyolefins such as polyvinylchloride, chlorinated polyethylene and chlorinated polypropylene are adversely affected when exposed to elevated temperatures either during fabrication or during use. This adverse eifect is usually evldencedby a darkening in color and an increase in viscosity Which is demonstrated by the increased work required to extrude or mix the material. It is generally believed that this change in viscosity is due to splitting hydrogen and/ or hydrogen chloride atoms out of the polymer molecule resulting in increased crosslinking of the polymer.

Many additives have been proposed which increase the thermal stability of specific halogen-containing polyolefins. However, there is no consistency in the effectiveness of these stabilizers when used in different types of halogen-containing polyolefins. For instance a number of compounds which effectively thermally stabilize vinyl chloride compounds have little or no stabilizing effect on chlorinated polyethylene. Another factor to be considered in the selection of a thermal stabilizer is the presence of a metal constituent in many of the prior art additives. These metal-containing stabilizers, such as metal salts, metal phenolates and organo-metallic compounds, are frequently incompatible with the polymer, causing loss of transparency, discoloration and nonhomogeneous appearance.

It is an object of the present invention to provide heat stable compositions based upon chlorinated polyethylenes.

Another object of the present invention is to provide metal-free organic stabilizers for chlorinated polyethylenes.

Additional objects and advantages of the present invention will become apparent from the following detailed description thereof.

In accordance with the present invention the thermal stability of chlorinated ethylene polymer is improved by the addition thereto of melamine pyrophosphate: /N H7NU/ CNH 1; H4P2O7 l 2 NH, This stabilizer is effective when added to chlorinated polyethylene in amounts equal to at least about 0.5 percent by weight of the polymer, with optimum results being obtained when the stabilizer is added in amounts equal to about 1 to 10 percent by Weight of the polymer.

The ability of melamine pyrophosphate to stabilize chlorinated polyethylene does not appear to be the result of any mechanism which is presently understood and other melamine compounds have been found to possess little or no stabilizing eifect. Among the melamine compounds which were found to be ineffective as stabilizers are N,N- dimethylrnelamine; N,N',N"-trimethyl melamine; N,N', N"-tri-n-butyl melamine; hexa-n-butyl melamine; and N,N-diallylmelamine.

The stabilizers can be employed with other common additives used in halogenated polyolefin formulations, such as stabilizers against the elfects of radiation, fillers, pigments, and dyes. The stabilizer can be incorporated into the polymer formulation by any known blending techmque.

The effectiveness of these stabilizers can be measured 7 by determination of the extent of crosslinking which is occasioned in the polymer by exposure to elevated temperatures. This crosslinking can be measured by the amount of gel formation. The latter can be determined as the percentage of the polymer, originally entirely soluble in monochlorobenzene, which is no longer soluble after the heat treatment. Gel formation increases viscosity and slows the rate of extrusion of the polymer if the extrusion is carried out at a constant pressure on the polymer.

A further measure of efiectiveness of stabilization is the comparison of color of the unstabilized material with that of the stabilized material after both have been exposed to elevated temperatures.

The chlorinated polyethylene stabilized by our invention can contain from about 20 to about 80% by weight chlorine. In a preferred embodiment, the chlorinated polyethylene is randomly chlorinated where it is essentially amorphous and has a low brittle point (glass transition temperature), such as about 0 C. or lower at 20 percent chlorine content and rising with chlorine content to over 185 C. at percent chlorine content. Particularly suitable polyethylenes to be chlorinated for use in our invention are those produced as described in Example 6 of British Patent No. 858,674, of J an. 11, 1961. Such polyethylenes can be chlorinated with advantage for use in our invention by the process described in Example 3 of French- Patent No. 1,316,044 of Dec. 17, 1962.

The polymerization process of British Patent No. 858,674 results generally in a polymer of high molecular weight such as 500,000 to 5,000,000 average molecular weight, and of density of about 0.935 to 0.96 gm./cm. at 25 C. The molecular weight of the polymer can be reduced by a thermal treatment, for instance in accordance with the process outlined at page 12, lines 73-77 of the above-identified British Patent No. 858,674. The molecular weight of the resulting polyethylenes will be in the range of about 20,000 to 300,000, and the density will be about 0.94-0.985 gm./cm. at 25 C.

The foregoing molecular weights are calculated from the intrinsic viscosity of a solution of the polymer in Decalin, according to the method of P. S. Francis et al. (Journal of Polymer Science, vol. 31, pp. 453-466), i.e., by using the following formula:

where [17] is the intrinsic viscosity in deciliters per gram, and M is the average molecular weight.

When polyethylenes of molecular weights such as 100,000 and below are chlorinated for use in our invention, solution chlorination methods can be used to advantage to obtain the desired amorphous products.

The glass transition temperatures above cited can be determined by a standard test for stillness (ASTM test -l0436lT), as the temperature below which the stiff ness sharply increases so that the sample becomes brittle. A typical stiffness modulus at the glass transition temperature for the subject chlorinated polyethylenes is 1.45 l0 p.s.i. (i.e., l0 dynes/cm.

One preferred group of randomly chlorinated polyethylenes of chlorine content in the range 20-80 percent by Weight used in our invention, will have relatively high intrinsic viscosities from about 1.5 to about 5 deciliters per gram, indicating high molecular weight. Other useful and preferred chlorinated polyethylenes, not necessarily amorphous, will have intrinsic viscosities from about 0.1

to about 1.5'deciliters per gram, indicating lower molecular weight of the polymer. These intrinsic viscosities are determined upon a 0.1 gram per 100 ml. solution in odichlorobenzene at 100 C.

The following examples describe completely specific embodiments of our invention and illustrate the best mode contemplated by us of carrying out our invention; but are not to be interpreted as limiting the invention to all details of the samples.

The samples tested consisted of unstabilized controls and compositions containing stabilizer in an amount equal to 4% by Weight of the weight of the chlorinated polyethylene. In all tests the chlorinated polyethylene sample was ground to about 40 mesh powder. The stabilizer was dissolved in a volatile solvent, such as methanol. This solution was added to the powdered polymer and the mixture was stirred under N at ambient temperatures, until completely dried.

About 23 grams of each prepared sample were heated in open test tubes in a block heater at 200 C. for 60 minutes, except where specified otherwise. This heat treatment of the'sample resulted in the thermal breakdown of the polymer into a certain percentage of a crosslinked product, or gel; as Well as resulting in a discoloration of the polymer, manifested by darkening. The quantitative value of the discoloration was measured using a reflectance meter with a green filter, by comparing the reflectance of the sample to that of a standard white magnesium oxide sample. The reflectance reading obtained on the discolored sample was thenexpressed as percent whiteness, the 3g reflectance of the standard being taken as 100% whiteness.

The amount of crosslinked product or gel formed as a result of the heat treatment was determined in accordance with the following procedure.

About 0.2 to 0.3 gram of the heat treated polymer was weighed into a tared stainless steel basket made of 250 mesh screen. This basket was placed into a Soxhlet extractor containing approximately 125 ml. monochlorobenzene, and refluxed for six hours. The non-crosslinked product was extracted, permitting gravimetric determination of the crosslink'ed gel. During the extraction the system was kept under slow N stream to prevent oxidation.

- Example In Table 1 comparative test results are shown to demonstrate the effectiveness of the stabilizing qualities TABLE 1 Stabilizer 7 Percent Percent Gel Whiteness Unstabilized resin 12 34 Melamine pyrophosphate 17 3 We claim: 7

1. A composition comprising chlorinated polyethylene and melamine pyrophosphate.

2. The composition of claim 1, wherein said melamine pyrophosphate is present at a concentration of at least 0.5 percent by weight'ofsaid chlorinated polyethylene.

3. The composition of claim 2, wherein said chlorinated polyethylene contains 20 to percent by weight chlorine, and has an intrinsic viscosity of about 0.1 to 5.0 in odichlorobenzene at C., and wherein the concentration of said melamine pyrophosphate is 1 to 10 percent by weight of said chlorinated polyethylene.

4. The composition of claim 3, wherein said chlorinated polyethylene is a high molecular weight polymer with random chlorination, having an intrinsic viscosity in the range between 1.5 and 5 deciliters per gram, as measured in o-dichlorobenzene at 100 C.

7 References Cited UNITED STATES PATENTS 2,578,904 12/1951 Stamatofi 260-4595 X 2,581,360 1/1952 Costa et al 26045.7 3,084,135 4/1963 Scullin 26045.8 X

DONALD E. CZAIA, Primary Examiner.

L. J. BERCOVITZ, Examiner.

M. I. WELSH, Assistant Examiner. 

1. A COMPOSITION COMPRISING CHLORINATED POLYETHYLENE AND MELAMINE PYROPHOSPHATE. 